Light integrating means for photocell circuit



July 24, 1956 K. FRANK 2,756,349

LIGHT INTEGRATING MEANS FOR PHOTOCELL CIRCUIT Filed July 23, 1953CONTROL IRA/VJLl/CE/VT lL/IST/C FIG N93 TAAASLZ/CE/YT l I fLAsr/cSTREET-LIGHT F/G. N 2

RAWSLI/C IYT PLASTIC CONTPOL C/IPCl/l? PIP/0R l0 1 srnssr LIGHT a, eINVEN TOR.

KARL FRANK United States Patent LIGHT INTEGRATING MEANS FOR PHOTOCELLCIRCUIT Karl Frank, Garden City, N. Y., assignor to Micro Balancing,Inc., New Hyde Park, N. Y., a corporation of New York Application July23, 1953, Serial No. 369,854 4 Claims. (Cl. 250-239) This inventionrelates to light integrating means for photocell control circuits andmore particularly, to a light integrating cover for photocells in suchcircuits.

This invention is a continuation in part of my prior application S. N.305,645 for Automatic Street Lighting System, filed August 21, 1952.

That application discloses photocell control means for automatic controlof individual street lights. Such apparatus generally has a photocell toactuate the control circuit when the average light intensity decreasesat sundown to turn on the street light. My prior application disclosessignal integrating means including a source of heat and a thermostatcontrol. The purpose of the integrating means is to avoid spuriousresponses due to flashes of light such as lightning, automobile headlights and the like. Such apparatus generally has a window in the coverso that the light can pass through to the photocell. In order to avoiddirect sunlight on the photocell, the window is generally faced north.This provides a north light, which is not representative of the averagelight intensity, since the majority of the light comes from above andother directions. Furthermore, there may be artificial impediments onthe north side such as buildings or trees which may cause shadows anddistort the light The present invention provides an automatic streetlight control circuit having a translucent cover which integrates thelight received from all directions as well as from above. In oneembodiment, the cover is made of methyl methacrylate also known asPlexiglas or Lucite, or equivalent, and is sandblasted on the inside inorder to etch the inside surface so as to scatter the light received.The etching on the inside serves several purposes. One is to protect thephotocell from direct light, and another purpose is to scatter the lightso that it may travel through the Lucite and be picked up by thephotocell. Since light is received from all directions, the input to thephotocell will be an average or integrated version of the total lightintensity received from all directions as well as from above. Thetransmission of light through Lucite even around curves and bends is awell known phenomena.

Accordingly, a principal object of the invention is to provide new andimproved light integrating means.

Another obect of the invention is to provide new and improved lightintegrating means for photocell control circuits.

Another object is to provide cover means for automatic street lightingcontrol circuits which are adapted to receive light from all directionsand from above and which also serve to integrate said light and transmitit to a photocell.

Another object is to provide an automatic street light control systemcomprising a photocell, a control circuit responsive to said photocelland cover means for said photocell adapted to receive light from alldirections, and to integrate said light and transmit said light to thephotocell.

Other objects of the invention will be apparent from the foliowingspecification and drawings of which:

Figure 1 is a view partially in section showing a typical Patented July24, 1956 P ice conventional street light control system having a coverwith a window on one side.

Figure 2 is a sectional view of the light integrating cover of thepresent invention illustrating the transmission of light through andaround the cover.

Figure 3 is a sectional View taken along the lines 33 of Figure 2.

Referring to Figure 1, there is shown a conventional street lightingcontrol system which is a simplified version of that shown in myaforementioned patent application. Figure 1 shows a street light 10 ontop of which is mounted the light control units. The light control unitincludes a photocell 1 and a control circuit 2 connected to, andresponsive to the photocell to turn the street light 10 on and oif at acertain average light intensity. The cover 3 for the light controlcircuits transmits light only through the window 4. As previouslymentioned, the standard practice is to face the window toward the northin order to protect the photocell from direct sunlight. This procedurehas several disadvantages. In the first place, the north light is notrepresentative of the average light intensity. Secondly, there may bebuildings or trees on the north side which may further interfere withthe proper operation of the system. Therefore, it is seen that theconventional covers with the windows facing north provide a falseindication of the average light intensity, since the most representativelight comes from above.

Figures 2 and 3 show the system of the present invention. The cover 11is made of a translucent plastic such as Lucite and it is sandblasted oretched on its entire inside surface 12. The photocell 1 and the controlcircuit 2 may be the same as previously described.

The light integrating operation of the cover is as follows:

Assume a beam of light represented by the arrow 13 strikes the cover.The light will pass through to the inside surface of the cover 11 andwill be scattered in all directions by the sandblasted inside surface atthe point 14. Thereupon, the light will travel in both directionsthrough the Lucite being alternatively reflected from one side or theother of the cover as illustrated by the arrows 15, 16, 17 and so forth.

We have shown only one beam of light 13. However, it can be easilyvisualized that light may be received from all directions and that aninfinite number of light beams are continuously being scattered by theinside etched surface and that these light beams are then beingtransmitted through the Lucite cover according to the well knownphenomena of transmission of light through Lucite and similar materials.

The etching of the inside does not reflect all the light and someportion of the light will be transmitted through to the inside of thecover. The amount of light transmitted through the cover at any givenpoint, will be the integrated light intensity of the infinite number oflight beams which have been received from all directions, scattered andthence transmitted through the Lucite cover.

Therefore, the inside of the cover in front of the photocell at point 20will transmit to the photocell the average light intensity of all thelight received both from all sides and from the top.

Figure 3 shows a sectional view of Figure 2 taken along the lines 33.Figure 3 illustrates that the cover is circular in the horizontal planeand also illustrates reception of a light beam 21 which is scattered bythe inside surface at point 22 and thence travels around until itilluminates the photocell l.

The invention is not limited to the illustrated use for automatic streetlighting control circuits, but it may be used wherever it is desired toobtain an integrated light for use with photocells or for any otherpurpose. The

invention is not limited to the use of Lucite since it is intended tocover any equivalent material.

Certain subject matter shown in Figure 1 is being claimed in mycopending prior application aforementioned.

I claim:

l. A photocell, a street light control circuit connected to andresponsive to said photocell, and protective cover adapted to integratethe light received from substantially all directions and to guide saidlight to said photocell.

2. A photocell, a control circuit connected to and responsive to saidphotocell, and means to integrate the light received from substantiallyall directions and to transmit said light to said photocell comprising acylindrical translucent cover etched on the inside.

3. An automatic control system for street lights comprising a photocell,a control circuit responsive to said photocell, and cover means tointegrate the light input to said photocell.

4. An automatic control system for street lights comprising a photocell,a control circuit responsive to-said photocell, and means to integratethe light input to said photocell comprising a translucent plasticcylindrical cover sandblasted on the inside.

References Cited in the file of this patent UNITED STATES PATENTSWillcox Oct. 7, 1952

